JPH03174810A - Linear transmitter - Google Patents

Abstract

PURPOSE:To obtain a linear amplifier operated stably with high accuracy and excellent power efficiency by correcting the control of a power voltage depending on a difference signal of an envelope between an input modulation wave and an output side. CONSTITUTION:A directional coupler 13 and an envelope detection circuit 14 are provided as output detection means to obtain an envelope of a modulation wave outputted from a high frequency power amplifier 4, and a difference signal generating circuit 15, a DC amplifier 16 and a correction circuit 17 as means correcting an output signal of an envelope detection circuit 5 inputted to a DC voltage conversion circuit 7 depending on the difference between an output of the envelope detection circuit 14 and the envelope detection circuit 5 are provided. Then a control signal of the power voltage is corrected depending on a difference between an output envelope and an input envelope of the high frequency power amplifier 4 is corrected. Thus, a stable linear transmitter with excellent power supply efficiency and high accuracy is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is used for power amplification in a high frequency band. In particular, the present invention relates to a linear transmitter that amplifies a modulated wave whose envelope signal level changes greatly with high power efficiency.

The present invention provides a linear amplifier in which the power supply voltage of a high frequency power amplifier is controlled by the envelope of an input modulated wave, by correcting the control of the power supply voltage using a difference signal between the envelope of the input modulated wave and the envelope of the output side. , which increases the power efficiency of linear amplifiers and allows them to operate with high precision and stability.

[Conventional technology]

Traditionally, linear transmitters have an operating class of A or A.
A class B high frequency power amplifier is used. Such power amplifiers have the disadvantage that power efficiency decreases when the envelope of the input signal is small. For this reason, for example, in a portable radio device that uses a battery as a power source, there is a problem that the battery consumption is large and the usage time of the radio device is shortened.

The second example of the configuration of a conventional linear transmitter that solved this problem is
4 and 25.

The first conventional example shown in FIG. 24 is a highly efficient linear transmitter that was previously filed by the applicant of the present invention. Details of this transmitting device are disclosed in Japanese Patent Laid-Open No. 62-274906.

The analog signal or digital signal input to the input terminal l is modulated by the modulation section 2. A saturation type high frequency power amplifier 4 amplifies this linearly modulated wave and outputs it to an output terminal 9.

The high frequency power amplifier 4 includes a field effect transistor as an amplification element, and controls the drain voltage of the field effect transistor almost in proportion to the envelope of the input signal, so that the saturation output level of the high frequency power amplifier 4 is adjusted to the envelope of the input signal. make it follow.

With this kind of control, the high frequency power amplifier 4 can be operated as a linear amplifier while being kept in a highly efficient saturated state, so it is possible to significantly reduce the output distortion that occurs at an extremely high level in a normal saturation type amplifier. can.

Moreover, even when the input power of the high-frequency power amplifier 4 is small, by changing the drain voltage according to the change in the input power, the high-frequency power amplifier 4 can be operated in a substantially saturated state, resulting in high power efficiency. Deterioration can be prevented.

The drain voltage is supplied from a DC power supply terminal 8 via a DC voltage conversion circuit 7 configured with a DC-DC converter or a series control transistor. To control the drain voltage, the input modulated wave is branched by the directional coupler 3, its envelope signal is detected by the envelope detection circuit 5, and the output of the envelope detection circuit 5 is level-corrected by the correction circuit 6. The DC voltage conversion circuit 7 is controlled by this.

This conventional device can realize a linear amplifier using a highly efficient saturated high frequency power amplifier. For example, if we use a high-frequency power amplifier 4 with a power efficiency of 70% and a DC-DC converter with a power efficiency of 70% as the DC voltage conversion circuit 7, we can ideally use a linear amplifier with an overall efficiency of 49%. realizable.

The second conventional example shown in FIG. 25 is "Linear Amplification Using Envelope Feedback", Electronics Letters, Vol. 7, 197.
April 8, 1 (“LINEARAMPLIFI-CAT
ION USINGεNVELOPB FEEDBAC
K”, [Electron.

Lett, Vol, 7.8th April 1971
), which performs envelope feedback type linear amplification using the envelope of the input signal and the envelope of the output signal.

Here, the explanation will be made assuming that the modulation section is omitted and the modulated wave is input to the modulated wave input terminal 1'. This modulated wave is supplied to the high frequency power amplifier 4 via the variable gain amplifier 33. High frequency power amplifier 4 amplifies this modulated wave and outputs it to output terminal 9.

To correct the nonlinearity of the high frequency power amplifier 4, the gain of the variable gain amplifier 33 is controlled. For this purpose, the modulated wave input to the modulated wave input terminal 1' and the output of the high frequency power amplifier 4 are branched by a directional coupler 3.13 and supplied to an envelope detection circuit 5.14. The envelope detection circuit 5.14 detects the envelope of each input signal and supplies it to the difference signal generation circuit 31. The difference signal generation circuit 31 generates a difference signal between the envelope signals and controls the gain of the variable gain amplifier 33 via the DC amplifier 16.

This compensates for the nonlinearity of the high frequency power amplifier 4, amplifies a signal free of amplitude distortion, and outputs the amplified signal to the output terminal 9.

This linear amplifier detects both the input and output envelopes of the high frequency power amplifier 4 and performs negative feedback. Therefore, the influence of variations in amplifiers and the like is small.

[Problem to be solved by the invention]

However, the first conventional example described above has the disadvantage that stable and highly accurate linear amplification cannot be achieved because the characteristics of the high-frequency power amplifier change due to manufacturing variations in the high-frequency power amplifier, temperature changes, and other causes. Ta.

In addition, in the second conventional example, the influence of variations in the high-frequency power amplifier is small, but the power supply efficiency is low when using batteries, and the gain of the difference signal amplification must be increased in order to reduce amplitude distortion. was there. For example, in order to reduce the amplitude distortion to 40 dB or less, it is necessary to amplify the difference signal to 40 dB or more.

The difference signal includes the DC signal up to the maximum frequency of the modulated wave envelope, and requires a DC amplifier. It is very difficult to accurately design a DC amplifier of about 40 dB considering temperature characteristics, and
There is a drawback that an error signal is generated due to such reasons.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a linear amplifier that is highly power efficient, operates stably with high precision.

[Means to solve the problem]

The linear amplifier of the present invention controls the power supply terminal voltage of a high frequency power amplifier that receives a modulated wave as an input signal according to the envelope of the input signal, and further provides a power supply voltage control signal using a difference signal between the input and output of the high frequency power amplifier. It is characterized by correcting.

It is desirable to include a frequency equalization circuit that equalizes the amplitude and phase of the corrected control signal and supplies the same to the DC voltage conversion circuit.

In addition, it can be used separately from the frequency equalization circuit or in combination with the frequency equalization circuit to maintain the output voltage of the DC voltage conversion circuit above a certain value when the signal level of the corrected control signal is lower than a predetermined value. It is desirable to have one or both of the means for

In this specification, the power supply terminal of a high-frequency power amplifier refers to a terminal that supplies power to active elements constituting the high-frequency power amplifier. In other words, it is a terminal that can control the voltage of the collector electrode if the high frequency power amplifier is a bipolar transistor with a grounded emitter, or the voltage of the drain electrode if the high frequency power amplifier is a grounded source of a FET. Furthermore, it refers to the anode terminal of a vacuum tube.

Further, when the high frequency power amplifier is configured in multiple stages, only the power terminal of one of the stages may be controlled, or the power terminals of all the stages may be controlled.

[For production]

By changing the power supply voltage of the high frequency power amplifier according to the envelope of the input modulated wave, the power supply efficiency can be improved and the linearity of the saturated high frequency power amplifier can be improved. In the present invention, in order to further improve the control accuracy of the power supply voltage, the voltage control signal (a signal obtained from the envelope of the input modulated wave) is corrected using the difference signal between the input and output envelopes. Since the voltage is controlled, the output distortion is considerably reduced.Therefore, the closed loop gain of the difference signal is small, the error in the feedback system can be reduced, and the negative feedback system can operate stably.

Furthermore, when amplifying a signal with a fast modulation speed, a frequency equalization circuit is provided on the input side of the DC voltage conversion circuit. If a DC-DC converter is used as a DC voltage conversion circuit, its switching frequency is at most about 1 MHz, and its frequency band is about 3QkHz. Therefore, the modulation speed that can be linearly amplified is limited. If a frequency equalization circuit is provided in front of the direct current voltage conversion circuit, the frequency characteristics of the direct current voltage conversion circuit can be equivalently expanded, and higher speed modulated waves can be amplified.

In order to operate the active elements of a high frequency power amplifier, it is necessary to apply a bias voltage of a certain value or more.

However, when the signal level of the envelope for controlling the power supply voltage becomes smaller than a certain value, a voltage that does not cause the active element to operate may be applied. In such a case, distortion occurs in the amplified signal. To prevent this, the characteristics of the active elements are taken into account and the output voltage of the DC voltage conversion circuit is controlled so as not to fall below a predetermined voltage, and the amplifier is operated linearly.

〔Example〕

FIG. 1 shows the block configuration countries of the linear transmitter according to the first embodiment of the present invention.

This linear transmitter includes a high frequency power amplifier 4. This high frequency power amplifier 4 is a saturation type high frequency power amplifier as shown in the first conventional example, for example, and receives a modulated wave modulated by an analog signal or a digital signal from a modulated wave input terminal 1', and amplifies it. The output is output to the output terminal 9. This linear transmitter further includes a directional coupler 3 and an envelope detection circuit 5 as input detection means for determining the envelope of the modulated wave input to the high frequency power amplifier 4. A DC voltage conversion circuit 7 that controls the voltage supplied to the power supply terminal of the power amplifier 4 is provided.

Here, the feature of this embodiment is that it is equipped with a directional coupler 13 and an envelope detection circuit 14 as an output detection means for determining the envelope of the modulated wave outputted by the high frequency power amplifier 4. 14 output and envelope detection circuit 5
A difference signal generation circuit 15, a DC amplifier 16, and a correction circuit 17 are provided as means for correcting the output signal of the envelope detection circuit 5 input to the DC voltage conversion circuit 7 based on the difference between the output signal and the output of the DC voltage conversion circuit 7.

The directional coupler 3 branches the input signal of the high frequency power amplifier 4, and the envelope detection circuit 5 detects the envelope of the signal.

Further, on the output side of the high frequency power amplifier 4, the output signal is branched by the directional coupler 13, and the envelope of the signal is detected by the envelope detection circuit 14.

The input-side envelope signal output from the envelope detection circuit 5 is supplied to the DC voltage conversion circuit 7 via the correction circuit 17 as a voltage control signal. The DC voltage conversion circuit 7 converts the voltage supplied from the DC power supply terminal 8 into DC and outputs a voltage that substantially follows the envelope line on the input side. This voltage output is supplied to the power supply terminal of the high frequency power amplifier 4 to obtain a high frequency output proportional to the envelope line.

Through the above-described operation, the operation of the high-frequency power amplifier 4 becomes a linear operation, and amplification with little distortion can be performed. Moreover, the power supply efficiency as a linear amplifier is improved by the DC voltage conversion circuit 7.

By the way, the characteristics of the -M high frequency power amplifier vary depending on manufacturing variations and ambient temperature.

In order to improve this, the envelope curve on the output side is compared with the envelope curve on the input side, and the control signal to the DC voltage conversion circuit 7 is corrected. That is, the error of the output with respect to the input is determined by the difference signal generation circuit 15, and the error is determined by the correction circuit 1 via the DC amplifier 16.
Supply to 7. The correction circuit 17 corrects the control signal supplied from the envelope detection circuit 5 to the DC voltage conversion circuit 7 based on the output of the DC amplifier 16. As the correction circuit 17, an arithmetic circuit that performs addition or subtraction is used to reduce or increase the envelope signal on the input side so that the amplitude characteristic of the high frequency power amplifier 4 becomes linear.

In such a configuration, when suppressing distortion by 50 dB, for example, distortion suppression of about 20 to 30 dB is possible by controlling the power supply voltage using the output of the envelope line detection circuit 5 on the input side. A distortion suppression amount of about 20 to 30 dB is sufficient. Therefore, the gain required of the DC amplifier 16 is about 20 to 30 dB at most.

In contrast, a conventional configuration using only envelope feedback requires a loop gain of 50 dB. In this way, this embodiment can utilize a very stable negative feedback system with a small loop gain.

FIGS. 2 to 4 show the difference signal generation circuit 15,
An example of the circuit configuration of the DC amplifier 16 and the correction circuit 17 is shown.

The difference signal generation circuit 15 includes input terminals 151, 152 and output terminals 158, and includes an operational amplifier 156 and a resistor 153.
154, 155 and 157. The input terminals 151 and 152 are supplied with the output of the envelope detection circuit 5.14. The signals at input terminals 151 and 152 are fed to an operational amplifier 156 via resistors 153 and 154, respectively. The non-inverting input of the operational amplifier 156 is connected to the resistor 15.
5 to ground, and the output is connected to the inverting input via a resistor 157.

The DC amplifier 16 has an input terminal 162 and an output terminal 168.
, an operational amplifier 166 and a resistor 163.164.16
5 and 167. Input terminal 162
is supplied with the output of the difference signal generation circuit 15, and the resistor 164 is supplied with the output of the difference signal generation circuit 15.
to the non-inverting input of operational amplifier 166.

The non-inverting input of operational amplifier 166 is further connected to ground via resistor 165. The inverting input of operational amplifier 166 is grounded via resistor 163, and the output is connected to the inverting input via resistor 167.

The correction circuit 17 includes an input terminal 171, 172 and an output terminal 178, and includes an operational amplifier 176 and a resistor 173, 174.
．． 175.177. Input terminal 17
1.172 shows the output of the envelope detection circuit 5 and the DC amplifier 1.
6 outputs are supplied. The signals at input terminals 171 and 172 are fed to an operational amplifier 176 via resistors 173 and 174, respectively. The non-inverting input of operational amplifier 176 is connected to ground via resistor 175, and the output is connected to the inverting input via resistor 177.

FIG. 5 is a block diagram showing a linear transmitter according to a second embodiment of the present invention.

This embodiment differs from the first embodiment in that digital arithmetic processing in the baseband band is used to obtain the envelope of the modulated wave input to the high frequency power amplifier 4.

That is, the modulation section 20 includes a complex envelope generation circuit 21 as an input detection means for determining the envelope of the modulated wave input to the high frequency power amplifier 4, and the envelope generation circuit 1
00 and a digital-to-analog converter 102.

A baseband signal is input to the input terminal 1 , this signal is modulated by the modulation section 20 , and the modulated wave is supplied to the high frequency power amplifier 4 . The modulation section 20 includes a complex envelope generation circuit 21, digital-to-analog converters 22 and 23, a quadrature modulator 24, and a carrier wave oscillator 25.

First, the operations of the complex envelope generation circuit 21, digital-to-analog converters 22, 23, quadrature modulator 24, and carrier wave oscillator 25 will be explained. These circuits are known circuits that generate modulated signals whose envelope line and phase change. For example, Tokihiro Miyo, Mitsuhiro Ono, and Tatsuya Aono, "Development of a Variable Baud Rate QPSK Modulator," Electronic Information, 1986. An example of its use is shown in Proceedings of the Spring National Conference of the Communication Society, Volume B-1, Paper No. 5O-3-2.

Here, the carrier wave angular frequency of the modulated wave is ω. , the envelope signal is R(t), and the modulation phase is φ(1), then the modulated wave e (
t) is generally expressed as e (t) = R(t) ・Re (exp[jφ(
t) ] ・exp [j ωct ] ]=Re (
It is expressed as E(t) ・exp[j ωCtko] (1). However, ReCf] represents the real part of the function f. E(t) is the complex envelope and E(t)=I
(t) −j Q(t) ・ (2)
It is expressed as I (t) and Q (t) are called an in-phase envelope component and a quadrature envelope component, respectively.

The complex envelope generation circuit 21 calculates the values of the in-phase envelope component I (t) and the orthogonal envelope component Q (t) according to the modulation input from the input terminal 1 by digital processing. These calculated values are transferred to the digital/analog converter 2.
By converting to an analog voltage in 2.23, I (
t) and Q (t) waveforms are obtained. These waveforms are input to the quadrature modulator 24. This quadrature modulator 24 is
By multiplying (t) and Q (t) by the in-phase carrier wave and orthogonal carrier wave, respectively, and adding these, e (t)
seek.

The envelope generation circuit 100 uses the complex envelope generated by the complex envelope generation circuit 21, that is, the values of I (t) and Q (t), to determine the envelope R of the modulated wave input to the high frequency power amplifier 4. (t), R(t)−[:I(t)2+Q(t)2)”
Find (4). This envelope R(t) is obtained by digital signal processing, and is output to the digital-to-analog converter 102 either as is or after some correction has been performed. The digital-to-analog converter 102 converts this signal into a digital signal and supplies it to the DC voltage conversion circuit 7 via the correction circuit 17.

The correction circuit 17 and the DC voltage conversion circuit 7 are the same as those shown in the first embodiment. That is, the correction circuit 17 corrects the signal supplied from the digital-to-analog converter 102, and the DC voltage conversion circuit 7 converts the DC voltage supplied from the DC 74m terminal 8 into DC/DC according to the output signal of the correction circuit 17. By doing so, the high frequency power amplifier 4
control the power supply voltage.

As described above, in this embodiment, since the envelope signal for power supply control is generated by digital signal processing, a highly accurate and stable signal can be generated.

As in the first embodiment, the output signal of the high frequency power amplifier 4 is branched by the directional coupler 13, and an output envelope is generated by the envelope detection circuit 14 and input to the difference signal generation circuit 15.

In the first embodiment, both input and output envelopes are detected from modulated waves, so even if the semiconductor element used in the envelope detection circuit 5.14 has nonlinear characteristics, it can be canceled out when generating the difference signal. . On the other hand, in the second embodiment,
The envelope line on the output side includes the influence of the nonlinear characteristics of the envelope detection circuit 14, and the envelope line on the input side is a linear signal. Therefore, two envelopes cannot be directly compared. To accurately compare two envelopes, the envelope detection circuit 14
It is necessary to cancel the nonlinear characteristics of

Therefore, in the second embodiment, the digital-to-analog converter 1
02 and the difference signal generation circuit 15, the envelope detection circuit 1
A signal conversion circuit 18 having the same configuration as 4 or a configuration capable of realizing the same characteristics is inserted. This signal conversion circuit 18 converts the output of the difference signal generation circuit 15 into the envelope detection circuit 14.
The influence of the detection characteristics of is canceled out, and the difference between the input envelope signal and the output envelope signal is output.

The output of the difference signal generation circuit 15 is amplified by a DC amplifier 16 and input to a correction circuit 17. The correction circuit 17 corrects the output of the digital-to-analog converter 102,
It is input to the current-voltage conversion circuit 7. These operations are equivalent to those in the first embodiment.

By controlling the power supply voltage as described above, it is possible to realize a linear amplifier that has excellent power supply efficiency, high precision, and operates stably.

FIGS. 6 and 7 show circuit diagrams of an example of the envelope detection circuit.

Conventionally, envelope detection circuits using diodes and transistors have been known.

FIG. 6 shows a circuit using diodes, and FIG. 7 shows a circuit using transistors.

In the circuit shown in FIG. 6, a modulated wave input terminal 1401 is connected to an anode terminal of a diode 1405 via a capacitor 1402, and a cathode terminal of the diode 1405 is connected to an output terminal 1408. diode 1405
Further, a bias voltage from a power supply 1404 is supplied through resistors 1403 and 1407. diode 1
The output side of 405 is grounded via capacitor 1406.

The DC component of the modulated wave input to the modulated wave input terminal 1401 is cut by the capacitor 1402, and the DC component of the modulated wave input to the modulated wave input terminal 1401 is
405. At this time, only the component higher than the anode voltage of the diode 1405 energizes the capacitor 1406, and the carrier wave is half-wave rectified. Capacitor 1406 is
The carrier wave is bypassed and only the envelope is output to the output terminal 1408.

In the circuit shown in FIG. 7, a modulated wave input terminal 1411 is connected to the base terminal of a transistor 1413 via a DC cut capacitor 1412. Power terminal 1414
is grounded via base voltage bias resistors 1415 and 1416, and a connection point between the two resistors 1415 and 1416 is connected to the base terminal of the transistor 1413. A transistor 1413 is also inserted between the power supply terminal 1414 and the ground point via collector-emitter bias resistors 1417 and 1418. An AC bypass capacitor 1419 is connected in parallel to the bias stabilizing resistor 1418 so that only a DC component is applied. The collector terminal of the transistor 1413 is grounded via a capacitor 1420, and the collector terminal of the transistor 1413 is connected to the output terminal 1.
421.

The modulated wave input to the modulated wave input terminal 1411 is half-wave rectified by the diode characteristics between the base and emitter of the transistor 1413, and is output to the collector terminal. The carrier wave of this output is removed by a capacitor 1420, and only the envelope is outputted to an output terminal 1421. Similarly to the case of envelope detection using a diode, the diode characteristics between the base and emitter are superimposed on this output signal.

When envelope detection is performed on both the input and output sides as in the first embodiment, the diode characteristics can be canceled out at the output of the difference signal generation circuit 15 by using the same configuration and characteristics. On the other hand, in the case of the second embodiment, the envelope on the input side is obtained by calculating a complex envelope signal.

The envelope waveform in this case becomes highly accurate by increasing the number of bits for calculation. On the other hand, on the output side, a diode or transistor is used for detection. Therefore, the detected waveform includes a component due to the nonlinear characteristics of the diode, and it is not possible to directly generate a difference signal from the envelope on the input side. Therefore, a signal conversion circuit 18 having substantially the same DC characteristics as the envelope line detection circuit 14 on the output side is inserted between the digital/analog converter 102 and the difference signal generation circuit 15.

FIG. 8 shows an example of the diode characteristics, and FIG. 9 shows an example of the characteristics of the signal conversion circuit 18.

When the diode in the envelope detection circuit 14 exhibits the characteristics shown in FIG. Add bias voltage and input. At this time, the output of the signal conversion circuit 18 is:
An envelope signal having the nonlinear characteristics of a diode is output. By using this signal to generate a difference signal from the envelope signal on the output side, the diode characteristics are canceled out from the difference signal.

10 and 11 are circuit diagrams showing two examples of the signal conversion circuit 18. The circuit shown in FIG. 10 is a case where the circuit shown in FIG. 6 is used as the envelope detection circuit 14, and the DC cut capacitor 1402 of the circuit is
This is the same circuit from which . Furthermore, the circuit shown in FIG. 11 is a case where the circuit shown in FIG. 7 is used as the envelope detection circuit 14, and is the same circuit from which the DC cut capacitor 1412 is removed.

In this way, by making the semiconductor element used in the signal conversion circuit 18 substantially the same as that in the envelope detection circuit 14, a difference signal can be generated without error.

The presence or absence of carrier wave removal capacitors 1406 and 1420 does not affect the characteristics.

As explained above, the configuration of the second embodiment using the envelope detection circuit 14 and the signal conversion circuit 18 allows a more accurate envelope feedback system to be configured.

FIG. 12 is a block diagram showing a third embodiment of the invention, and FIG. 13 is a block diagram showing a fourth embodiment of the invention.

In the first and second embodiments described above, the configuration of the DC voltage conversion circuit 7 is such that extremely low frequencies are amplified in order to obtain a constant output with respect to the input voltage. Therefore, the input/output cutoff frequency is very small, 10K
It is about Hz. Therefore, in an amplifier for a modulated wave signal that fluctuates at a frequency higher than this cutoff frequency, the DC voltage conversion circuit 7 cannot follow changes in the modulated wave signal. As a result, distortion occurs in the output. For example, the frequency characteristics of a switching regulator depend on the control switch frequency and filter in the regulator. In order to improve this frequency characteristic, the control switch frequency may be increased, but the frequency is at most about 500 kHz due to the switching characteristics of the transistors and diodes that are the switches.

For this reason, it is difficult to obtain sufficient frequency characteristics, and as a result, it is not possible to realize a linear transmitter that is sufficient for a modulated wave signal with a high modulation frequency.

The third and fourth embodiments eliminate these drawbacks and equivalently widen the input/output frequency characteristics with a simple configuration.
This embodiment differs from the first embodiment and the second embodiment in that it includes a frequency equalization circuit 11 that equalizes the amplitude and phase of the control signal supplied to the control signal.

FIG. 14 is a circuit diagram showing details of the frequency equalization circuit 11.

This frequency equalization circuit 11 includes resistors R1 to R6, capacitors C1 and C2, and operational amplifiers 112 and 113.
It consists of: One ends of the resistors RI and R6 are connected to the input terminal 111, the other end of the resistor RI is commonly connected to the resistor R2, one end of the capacitors C3 and C2, the other end of the resistor R2 is grounded, and the other end of the capacitor CI is connected to the output of the operational amplifier 112 along with the other end of the resistor R5 and one end of the resistor R4, the other end of the capacitor C2 is connected to the inverting input terminal of the operational amplifier 112 along with one end of the resistor R5, and The terminal is grounded, and the other end of resistor R4 is connected to one end of resistor R5 and resistor R
The non-inverting input terminal of the operational amplifier 113 is grounded, and the output of the operational amplifier 113 is connected to the other end of the resistor R5 and the output terminal 114.

FIG. 15 shows an example of the spectrum of the envelope signal in the QPSK modulation method, that is, the envelope signal R(
t) is a characteristic diagram showing the frequency distribution. However, the roll off=0.5 and the transmission speed is 32 Kb/s. In order to suppress the amplitude distortion of the high frequency power amplifier 4 to 50 dB or less, the frequency characteristics of the DC voltage conversion circuit 7 must be
It is necessary to include up to 5 odt+low spectrum components.

Therefore, in this case, a band of approximately 40 to 50 KHz is required.

FIG. 16 shows an example of frequency equalization characteristics for obtaining this band. Curve A shows the frequency characteristics of the DC voltage conversion circuit 7 before frequency equalization, and its cutoff frequency is 10K) Iz or less. On the other hand, the frequency equalization circuit 11 has a frequency characteristic, as shown by curve B, in which the amplitude is large in the high frequency range. Therefore, when this equalized signal passes through the DC voltage conversion circuit 7, its characteristics become as shown by curve C. That is, the cutoff frequency is 50 KHz or more. The improved output voltage of the DC voltage conversion circuit 7 controls the drain voltage Vo of the high frequency power amplifier 4, making it possible to amplify a high-speed modulated wave signal.

The frequency equalization circuit 11 having such frequency characteristics is
As an example is shown in FIG. 14, it can be easily realized using an operational amplifier, a resistor, and a capacitor (see "Electronic Filter" by William, translated by Kato, McGraw-Hill Publishing).

FIG. 17 is a block diagram showing a fifth embodiment of the invention, and FIG. 18 is a block diagram showing a sixth embodiment of the invention.

The first feature of these embodiments is that the level conversion circuit 12 is provided as a means for maintaining the output voltage of the DC voltage conversion circuit 7 at a certain value or higher when the signal level of the envelope is smaller than a predetermined value. This is different from the embodiment and the second embodiment.

Figure 19 shows the high frequency power amplifier 4 for the high frequency input terminal.
An example of drain voltage characteristics with constant gain is shown below.

In FIG. 19, the dashed line indicates a certain value of the drain voltage (
The example in FIG. 19 shows a case in which the high frequency power amplifier 4 operates when the voltage is higher than about 2 V), and the relationship between the high frequency input voltage and the drain voltage is approximately linear.

In this case, the linearity of the high frequency power amplifier 4 can be maintained by amplifying the output of the envelope detection circuit 5 with an appropriate amplification factor and shifting its voltage level.

On the other hand, as shown by the solid line in Figure 19,
The drain voltage characteristics are nonlinear with respect to the high-frequency input terminal, and a substantially constant drain voltage may be required in a region where the input voltage is small. In such a case, the 19th
It is approximated by the broken line shown in the figure. That is, when the high frequency input voltage is V, or less, it is a constant value V. Approximately, when the input terminal exceeds V, a drain voltage that increases linearly with respect to the high frequency input voltage is required. FIG. 20 shows an example of a level conversion circuit for obtaining such characteristics.

The corrected envelope signal output from the correction circuit 17 is supplied to the input terminal 1201. This input terminal 1201 is connected to an inverting input of an operational amplifier 1203 via a resistor 1202. The non-inverting input of operational amplifier 1203 is grounded. The output of the operational amplifier 1203 is connected to the diode 120
4 and the cathode of diode 1205. The cathode of diode 1205 is connected to the inverting input of operational amplifier 1203. This inverting input is further supplied with a voltage -V via a resistor 1206.

The connection point between resistor 1206 and operational amplifier 1203 is resistor 1
208 to the anode of diode 1205. The anode of the diode 1205 is further connected to a resistor 1
208 to the inverting input of operational amplifier 1209. A voltage Va is supplied to the non-inverting input of the operational amplifier 1209. The output of the operational amplifier 1209 is connected to the resistor 121
It is feedback-connected to the inverting input via the output terminal 1211 and output to the DC voltage conversion circuit 7 via the output terminal 1211.

When the signal level of the input terminal 1201 is lower than the voltage Vs, the diode 1204 becomes conductive, the diode 12o5 becomes non-conductive, and the operational amplifier 1203 becomes a positive phase amplifier with a gain of "1". Since the non-inverting input of operational amplifier 1203 is grounded, its output is at zero potential. Therefore, voltage -Vs is applied to resistor 1208 via resistors 1206 and 1207.

When the signal level of the input terminal 1201 exceeds the voltage V,
Diode 1204 becomes non-conductive, diode 1205 becomes conductive, and operational amplifier 1203 operates as an inverting amplifier.

The operational amplifier 1209 has an offset voltage V. is added to amplify the signal from resistor 1208. By supplying this amplified signal to the DC voltage conversion circuit 7 via the output terminal 1211, the drain bias voltage of the high frequency power amplifier 4 can be controlled as shown by the broken line in FIG. The slope when the high frequency input voltage exceeds V can be set by selecting the values of resistors 1207 and 1210.

In this way, even when the signal level of the envelope is low, the high frequency power amplifier 4 can be operated sufficiently, and an output signal with little distortion can be obtained.

FIG. 21 is a block diagram showing the seventh embodiment of the present invention, and FIG. 22 is a block diagram showing the eighth embodiment.

These embodiments differ from the first embodiment and the second embodiment in that they include a frequency equalization circuit 18 and a level conversion circuit 19. That is, the DC voltage conversion circuit 7 is controlled via the frequency equalization circuit 11 and the level conversion circuit 12. The point to be careful here is to perform level conversion after frequency equalization; doing the opposite has no effect. With such a configuration, more stable and highly accurate voltage control can be performed, and higher speed signals can be linearly amplified with low distortion and high efficiency.

FIG. 23 shows an example of the output power spectrum of the second embodiment. In this example, the modulation format is QPSK
is used. The vertical axis of the figure shows the power spectrum, and the horizontal axis shows the frequency. When a saturation type high-frequency power amplifier 4 is used and the drain voltage is not controlled and is operated only with DC voltage, when the drain voltage is controlled according to the envelope on the input side, and when the drain voltage is controlled and the output side The respective outputs are shown when feedback is applied using the envelope. It can be seen that the out-of-band sub-radiation (r±Δf, f±2Δf) is reduced by each distortion compensation.

In the above description, a DC-DC converter and a series control transistor are exemplified as the DC voltage conversion circuit 7 that controls DC voltage using a control signal. As the DC-DC converter, a DC voltage conversion circuit using pulse width modulation, which is usually called a class S amplifier, can be used. Further, there are step-down DC/DC converters and switching regulators that have very similar operating principles, and such DC voltage conversion circuits can be used.

Further, the present invention can be implemented in the same manner even when the input to the high frequency power amplifier is an intermediate frequency obtained by converting the frequency of a modulated wave.

〔Effect of the invention〕

As explained above, the linear amplifier of the present invention uses a saturated high-frequency power amplifier, controls the power supply voltage of the amplifier based on the envelope of the modulated wave, and calculates the difference between the output envelope and the input envelope of the power amplifier. The power supply voltage control signal is corrected by This has the effect of realizing a highly accurate and stable linear transmitter with good power supply efficiency.

Furthermore, when determining the envelope line from the baseband signal and using it as a control signal, a highly accurate control signal can be generated by canceling out the detection characteristics using a detector that is the same as or has the same characteristics as the detector for the output envelope.

Furthermore, by performing amplitude and phase equalization of the corrected signal, it is possible to linearly amplify the high-speed modulated wave, and when the corrected signal is smaller than a predetermined value, the signal is leveled to a signal above a certain level. By converting, stable operation can be achieved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a linear transmitter according to a first embodiment of the present invention. FIG. 2 is a circuit diagram showing an example of a difference signal generation circuit. FIG. 3 is a circuit diagram showing an example of a DC amplifier. FIG. 4 is a circuit diagram showing an example of a correction circuit. FIG. 5 is a block diagram showing a linear transmitter according to a second embodiment of the present invention. FIG. 6 is a circuit diagram showing an example of an envelope detection circuit. FIG. 7 is a circuit diagram showing another example of the envelope detection circuit. FIG. 8 is a diagram showing an example of diode characteristics. FIG. 9 is a diagram showing an example of characteristics of a signal conversion circuit. FIG. 10 is a diagram showing an example of a signal conversion circuit. FIG. 11 is a diagram showing another example of the signal conversion circuit. FIG. 12 is a block diagram showing a linear transmitter according to a third embodiment of the present invention. FIG. 13 is a block diagram showing a linear transmitter according to a fourth embodiment of the present invention. FIG. 14 is a circuit diagram showing an example of a frequency equalization circuit. FIG. 15 is a diagram showing an example of an envelope spectrum. FIG. 16 is a diagram showing an example of frequency characteristics. FIG. 17 is a block diagram showing a linear transmitter according to a fifth embodiment of the present invention. FIG. 18 is a block diagram showing a linear transmitter according to a sixth embodiment of the present invention. FIG. 19 is a diagram showing an example of drain voltage characteristics in which the gain of the high-frequency power amplifier is constant with respect to the high-frequency input voltage. FIG. 20 is a circuit diagram showing an example of a level conversion circuit. FIG. 21 is a block diagram showing a linear transmitter according to a seventh embodiment of the present invention. FIG. 22 is a block diagram showing a linear transmitter according to an eighth embodiment of the present invention. FIG. 23 is a diagram showing an example of the output power spectrum of the second embodiment. FIG. 24 is a block diagram showing a first example of a conventional linear transmitter. FIG. 25 is a block diagram showing a second example of a conventional linear transmitter. 1...Input terminal, 1'...Modulated wave input terminal, 2.2
0... Modulation unit, 3.13... Directional coupler, 4...
・High frequency power amplifier, 5.14...Envelope detection circuit,
6.17... Correction circuit, 7... DC voltage conversion circuit,
8...DC power supply terminal, 9...Output terminal, 11...
Frequency equalization circuit, 12...Level conversion circuit, 15...
- Difference signal generation circuit, 16... DC amplifier, 18...
Signal conversion circuit, 21... complex envelope generation circuit, 22.
23.102...Digital-to-analog converter, 24
... Quadrature modulator, 25 ... Carrier wave oscillator, 100.
...Envelope generation circuit.

Claims (1)

[Claims] 1. A high-frequency power amplifier, an input detection means for determining the envelope of a modulated wave input to the high-frequency power amplifier, and an output signal of the input detection means supplied to a power supply terminal of the high-frequency power amplifier. A linear transmitting device comprising: a DC voltage conversion circuit for controlling a voltage output from the high-frequency power amplifier; A linear transmitter comprising means for correcting an output signal of the input detection means input to the DC voltage conversion circuit based on a difference between the output signal and the output voltage. 2. The linear transmitter according to claim 1, further comprising a frequency equalization circuit that equalizes the amplitude and phase of the signal outputted by the correcting means and supplies the same to the DC voltage conversion circuit. 3. The linear transmitter according to claim 1, further comprising means for maintaining the output voltage of the DC voltage conversion circuit above a certain value when the output signal level of the correcting means is smaller than a predetermined value.